The present invention relates to a dielectric porcelain and a dielectric resonator which show a high relative dielectric constant xcex5r and a high Q factor, that indicates a high selectivity of resonance, in high frequency regions such as microwaves and millimeter waves, for example, to a dielectric porcelain suitable for forming high frequency electronic components such as dielectric resonator, dielectric substrate material for MIC (monolithic IC), dielectric waveguide material and laminated ceramic capacitor, and to a dielectric resonator using the same.
Dielectric porcelains have been widely used in dielectric resonators, dielectric substrate for MIC and waveguide that are used in high frequency applications such as microwave and millimeter waves. Three major requirements for the dielectric porcelain are as follows.
(1) The material must have a high relative dielectric constant when used to make a small-sized component, since the electromagnetic wave propagating in a dielectric material has a wavelength reduced to (1/xcex5r)1/2.
(2) The material must have less dielectric loss, namely a high Q factor, at high frequencies.
(3) Resonant frequency of the material must be subject to less variation when the temperature changes, that is, the relative dielectric constant xcex5r must be stable with less temperature dependency.
As a dielectric porcelain that satisfies these requirements, for example, Japanese Unexamined Patent Publication (Kokai) No. 4-118807 discloses a dielectric porcelain based on CaOxe2x80x94TiO2xe2x80x94Nb2O5xe2x80x94DO (D represents an element such as Zn, Mg, Co, Mn, etc.) But this dielectric porcelain has Q factor as low as 1600 to 25000 when converted to values at 1 GHz, and temperature coefficient xcfx84f of the resonant frequency as high as 215 to 835 ppm/xc2x0 C., thus there has been a demand to improve the Q factor and decrease the value of xcfx84f.
To address the problems described above, the applicant of the present application has previously proposed a dielectric porcelain based on LnAlCaTi (Japanese Unexamined Patent Publication (Kokai) No. 6-76633; Ln represents a rare earth element), a dielectric porcelain based on LnAlSrCaTi (Japanese Unexamined Patent Publication (Kokai) No. 11-278927) and a dielectric porcelain based on LnAlCaSrBaTi (Japanese Unexamined Patent Publication (Kokai) No. 11-106255).
Meanwhile Japanese Unexamined Patent Publication (Kokai) No. 2-192460 discloses a dielectric porcelain consisting of TiO2xe2x80x94ZrO2xe2x80x94SnO2 as a main component with CoO and Nb2O5 added thereto.
However, the dielectric porcelain based on LnAlCaTi (Japanese Unexamined Patent Publication (Kokai) No. 6-76633; Ln represents a rare earth element) has such a problem that the Q factor ranges from 20000 to 58000 in a range of relative dielectric constant xcex5r from 30 to 47, and can become less than 35000, and therefore there has been a demand to improve the Q factor.
The dielectric porcelain based on LnAlSrCaTi (Japanese Unexamined Patent Publication (Kokai) No. 11-278927) has such a problem that the Q factor ranges from 20000 to 75000 in a range of relative dielectric constant xcex5r from 30 to 48, and can become less than 35000, and therefore there has been a demand to improve the Q factor.
The dielectric porcelain based on LnAlCaSrBaTi (Japanese Unexamined Patent Publication (Kokai) No. 11-106255) has such a problem that the Q factor ranges from 30000 to 68000 in a range of relative dielectric constant xcex5r from 31 to 47, and can become less than 35000, and therefore there has been a demand to improve the Q factor.
Although the dielectric porcelain based on TiO2xe2x80x94ZrO2xe2x80x94SnO2 allow it to improve the Q factor by adding such additive as CoO or Nb2O5 as disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2-192460, there has been such problems as the addition of an additive leads to an increase in the material cost, complicated manufacturing process and the necessity to control the firing atmosphere, thus increasing the manufacturing cost.
A main object of the present invention is to provide a dielectric porcelain that has a Q factor not less than 43000 in a range of relative dielectric constant xcex5r from 30 to 48, particularly a dielectric porcelain which has a high value of Q factor not less than 46000 in a range of relative dielectric constant xcex5r not less than 40 with the relative dielectric constant xcex5r being stable and less dependent on the temperature, and a dielectric resonator using the same.
The dielectric porcelain of the present invention, which achieves the object described above, comprises a polycrystalline material comprising of oxides, as a main component, containing at least a rare earth element (Ln), Al, M (M represents at least one selected from Ca and Sr) and Ti as metal elements, wherein the thickness of a grain boundary layer is 20 nm or less. According to the present invention, it possible to improve the Q factor.
The thickness of the grain boundary layer can be made not larger than 20 nm by manufacturing the dielectric porcelain in a process that uses, for example, an oxide of a rare earth element (Ln) and an Al oxide made in ultra-fine powder by using a nitrate or the like as the starting material.
It is desirable that at least a part of the oxide of Al is included in the form of crystal consisting of at least one kind selected from a group of xcex1-Al2O3, xcex2-Al2O3 and xcex8-Al2O3.
The dielectric porcelain of the present invention preferably comprises of oxides, as a main component, containing at least a rare earth element (Ln), Al, M (M represents Ca and/or Sr) and Ti as metal elements, and in case that a compositional formula of the oxides is represented by aLn2Ox.bAl2O3.cMO.dTiO2 (3xe2x89xa6xxe2x89xa64), molar ratios a, b, c and d satisfy the following relationships:
0.056xe2x89xa6axe2x89xa60.214;
0.056xe2x89xa6bxe2x89xa60.214;
0.286xe2x89xa6cxe2x89xa60.500;
0.230 less than d less than 0.470;
and
a+b+c+d=1.
The dielectric porcelain of the present invention preferably contains at least one of metal elements Mn, W, Nb and Ta in the total amount of 0.01 to 3% by weight on the basis of MnO2, WO3, Nb2O5 and Ta2O5.
The dielectric resonator of the present invention preferably comprises oxides, as a main component, containing at least a rare earth element (Ln), Al, M (M represents at least one selected from Ca and Sr) and Ti as metal elements, a half width of a peak observed in a range from 700 to 900 cmxe2x88x921 of laser Raman spectrum being 120 cmxe2x88x921 or less. The dielectric resonator may contain at least one of metal elements Mn, W, Nb and Ta in the total amount of 0.01 to 3% by weight on the basis of MnO2, WO3, Nb2O5 and Ta2O5.
According to the invention, the Q factor of the dielectric porcelain can be improved by making the material have a peak having half width of 120 cmxe2x88x921 or less in a range from 700 to 900 cmxe2x88x921 of laser Raman spectrum. When the dielectric porcelain is manufactured by forming a material prepared by a hydrothermal synthesis method, a metal alkoxide method or a coprecipitation method into a preform and firing the preform at a temperature in a range from 1550 to 1650xc2x0 C. for 5 to 10 hours, the half width of the peak observed in a range from 700 to 900 cmxe2x88x921 of laser Raman spectrograph can be made not greater than 120 cmxe2x88x921.
Another dielectric resonator of the present invention comprises oxides, as a main component, containing at least Ti, Zr and Sn as metal elements and shows a peak having half width of 120 cmxe2x88x921 or Less in a range from 700 to 900 cmxe2x88x921 of laser Raman spectrum.
The dielectric porcelain preferably comprises oxides, as a main component, containing at least Ti, Zr and Sn as metal elements, and in case that a compositional formula of the oxides is represented by hTiO2.iZrO2.jSnO2, molar ratios h, i and j satisfy the following relationships:
0.30xe2x89xa6hxe2x89xa60.60;
0.25xe2x89xa6ixe2x89xa60.60;
0.025xe2x89xa6jxe2x89xa60.20;
and
h+i+j=1.
The dielectric resonator of the present invention is made by disposing the dielectric porcelain described above between a pair of input and output terminals so as to function through electromagnetic coupling.
Other objects and advantages of the present invention will be made apparent from the following description.